This invention relates generally to internal combustion engines. More specifically, the present invention relates to a cylinder head comprising one or more replaceable combustion chamber domes supported within a fluid-cooled housing.
Two cycle internal combustion (IC) engines are characterized by one or more cylinders consisting essentially of cylindrical bores within an engine or cylinder block. A piston fits within the cylinder such that it can move reciprocally. One end of the cylinder is closed by a cylinder head to establish a combustion chamber between a top of the piston and the cylinder head. The two cycle cylinder construction differs from four cycle cylinder construction in that the latter incorporates intake and exhaust valves in the cylinder head while the two cycle engine has intake and exhaust ports in a wall of the cylinder.
When the piston is reciprocated to its lowest position in the cylinder, the maximum volume of the cylinder is defined. The minimum cylinder volume is defined when the piston is at its highest position in the cylinder. The ratio of maximum volume to minimum volume is referred to as compression ratio. The greater the compression ratio, the more efficient the engine. In most IC engines, the cylinder head is manufactured with a shaped pocket or chamber which defines the cylinder volume at the highest piston position and therefore directly affects the performance of the engine.
While combustion chamber definition is the single most important function of the cylinder head, the head also serves to dissipate heat generated by the combustion process. For this reason, water cooled cylinder heads are generally manufactured in two sections by machine or the like.
There are many applications which require changes in cylinder head design. Such changes may be necessitated not only by a need to vary engine compression ratio but also to adapt an engine for different octane rated fuels or for different fuels. In particular, it is common practice to modify cylinder heads in order to develop high performance engines. In some situations, such as in racing, it is often desirable to be able to modify a cylinder head to obtain a performance characteristic suitable for immediate conditions.
Aftermarket cylinder heads are typically manufactured with either integrated domes as part of the cylinder head itself, or with replaceable domes. In the case of cylinder heads utilizing replaceable domes, several problems presently exist. In particular, such domes do not typically provide adequate cooling to both the cylinder head housing and the replaceable domes, and they often rotate during spark plug installation and/or removal.
By way of illustration, if during a touring trip a spark plug requires replacement and during that operation it is discovered that the replaceable dome turns without the plug being removed, the vehicle is unable to be operated further. It must be towed to a location where the cylinder head may be removed. The problem is exacerbated during races where the plugs must be removed and replaced several times. If such dome rotation occurs, the head must be removed, which could limit a racer's ability to arrive at the starting line on time.
With regard to the problem of adequately cooling the cylinder head and, particularly, the replaceable dome, typical cylinder head cooling/flow design does not allow for the distinct flow of coolant therethrough in a plurality of flow paths at different temperatures. Thus, the different cooling requirements of the cylinder head in contrast with that of the replaceable domes are not specifically addressed.
Accordingly, there has been a need for an improved cylinder head for an internal combustion engine wherein the replaceable dome is incapable of rotating relative to an engine cylinder head housing. Additionally, there exists a need for a novel cylinder head design including a plurality of isolated fluid coolant flow paths which enable the coolant which has been heated by the cylinder block to cool the engine cylinder head housing, but also permits the flow of fluid coolant about a combustion chamber dome prior to be directed to the cylinder block. The present invention fulfills these needs and provides other related advantages.